1. Field of the Invention
This invention relates to a ceramic, particularly to a ceramic which can be utilized as electronic materials including materials for electronic parts such as ceramic capacitors, etc., or electronic circuit substrates having electronic parts built therein such as capacitor built-in ceramic substrates, a method for producing the ceramic and also an electronic circuit substrate utilizing the ceramic.
2. Related Background Art
In the prior art, an electronic circuit substrate using ceramics is generally directed to an insulator substrate provided with conductor circuits and resistor portions, and electronic parts such as a capacitor are usually mounted as chip parts on such an insulator substrate. FIG. 1 shows an example of such an electronic circuit substrate, in which 121 is a ceramic insulator substrate, 122 a conductor circuit, 123 a resistor, 124 an insulating layer for a cover and 125 a chip capacitor.
However, when a chip part such as a capacitor is mounted externally of a substrate as shown in FIG. 1, the substrate becomes bulky and restrictions will be naturally imposed on circuit design in order to ensure the mounting site for the chip part. Accordingly, such a construction cannot sufficiently cope with the demand for miniaturization of electronic circuits in recent years.
On the other hand, as to an electronic part using ceramics, for example, the technique for producing a solid capacitor which primarily uses a barium titanate type sintered product porcelain has been developed, where starting materials are subjected to primary calcination with impurities to be made into a semiconductor and then subjected to secondary calcination using as a diffusion source a metal or a metal oxide to be converted into a dielectric. However, concerning the application of such a capacitor, no technique for assembling a plural number of capacitors into a single circuit substrate has been established except for using this technique as a chip. Thus, under the present situation, it has not sufficiently contributed to miniaturization of a circuit substrate.
Also, as to a capacitor of this kind, it is known as an example in recent years that the technique of a laminated ceramic capacitor has been developed and a resistor-and-capacitor built-in substrate is fabricated by mounting conductor circuits and resistor portions on its surface. In such a substrate, the characteristic range of a capacitor which can be built in is restricted by the dielectric material constituting the substrate. If desired circuit constants are within the range of this restriction, the use of such a substrate is very effective in miniaturization of electronic circuit.
However, this substrate involves serious drawbacks.
The first problem is cost. More specifically, since the means for forming a capacitor involves the lamination of ceramics, the production equipment is cumbersome, whereby a large number of steps are required. Also, it is necessary to employ a large amount of relatively expensive electrode materials.
The next problem relates to circuit constitution.
In the case of forming a plural number of capacitor constituting units within a single substrate, they must be formed by laminating plural kinds of dielectric materials in combination. However, the types of circuits to which this technique can be applied have been limited.
Further, in a laminated ceramic capacitor, two thru-holes are required for one capacitor unit. For this reason, a capacitor built-in substrate of this type has a very large number of thru-holes, thus having the drawback of leading to the increase of substrate area.
FIG. 2 shows a ceramic substrate of this type, in which 121-123 have the same meanings as in FIG. 1, 126 and 127 are laminated type capacitor constituting units built in the substrate, 128 is a chip part mounted on the substrate and 129 is a thru-hole.
Thus, also in the case of providing a plurality of capacitor units built in a substrate through utilization of a laminated ceramic capacitor, there are serious restrictions not only with respect to the cost, but also with respect to the demand for circuit miniaturization and the degree of freedom in circuit design.